Cathode active material for non-aqueous electrolyte secondary battery and manufacturing method thereof

ABSTRACT

The purpose of the present invention is to easily provide at low cost, a cathode active material for non-aqueous electrolyte secondary batteries, which exhibits high particle strength and high weather resistance, while enabling achievement of excellent charge and discharge capacity and excellent output characteristics in cases where the cathode active material is used as a cathode material of a non-aqueous electrolyte secondary battery. A slurry of from 500 g/L to 2000 g/L is formed by adding water to a powder of a lithium nickel composite oxide represented by the general formula (A): Li z Ni 1-x-y Co x M y O 2 , where 0.10≦x≦0.20, 0≦y≦0.10, 0.97≦z≦1.20, and M represents at least one element selected from among Mn, V, Mg, Mo, Nb, Ti and Al); the slurry is washed with water by stirring; and after filtration, the resulting material is subjected to a heat treatment at a temperature of from 120° C. to 550° C. (inclusive) in an oxygen atmosphere having an oxygen concentration of 80% by volume or more.

TECHNICAL FIELD

The present invention relates to a cathode active material for anon-aqueous electrolyte secondary battery and manufacturing methodthereof.

BACKGROUND ART

In recent years, with the spread of portable electronic devices such asnotebook personal computers, cell phones and the like, there is a largeneed for development of compact and lightweight secondary batterieshaving a high energy density. Further, as a battery for an electricvehicle including a hybrid automobile, the development of a secondarybattery having high output characteristics is strongly desired. As anon-aqueous electrolyte secondary battery that satisfies such needs,there is a lithium-ion secondary battery. A lithium-ion secondarybattery has an anode, a cathode and an electrolyte, and as the activematerial of the anode and the cathode, a material is used for whichdesorption and adsorption of lithium is possible.

Currently, much research and development is being performed forlithium-ion secondary batteries, and particularly, lithium-ion batteriesthat use a layered or spinel type lithium composite oxide as the cathodeactive material can obtain a 4V class high voltage, so practicalapplication as a battery having high energy density is advancing.

As the lithium composite oxide that is used as the cathode activematerial of a lithium-ion secondary battery, currently, lithium cobaltcomposite oxide (LiCoO₂) for which the composition is comparativelysimple, lithium nickel composite oxide (LiNiO₂) that uses nickel that isless expensive than cobalt, lithium nickel cobalt manganese compositeoxide (LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂), lithium manganese composite oxide(LiMn₂O₄) that uses manganese and the like have been proposed.

Of these, lithium nickel composite oxide displays a large charge anddischarge capacity, so it is expected to become a cathode activematerial from which a secondary battery having high energy density canbe manufactured. However, pure lithium nickel composite oxide hasproblems with thermal stability and cycling characteristics in thecharging state, and thus use as a practical battery would be verydifficult.

Due to such a situation, an attempt was made to improve the thermalstability and cycling characteristics by replacing part of the nickel ofparticles of a lithium nickel composite oxide with other metal elements.For example, JPH05-242891 (A) discloses a lithium nickel composite oxidethat is expressed by the general formula: Li_(a)M_(b)Ni_(c)Co_(d)O_(e)(where M is at least one metal that is selected from among Al, Mn, Sn,In, Fe, V, Cu, Mg, Ti, Zn and Mo, and 0≦a≦1.3, 0.02≦b 0.5,0.02≦d/c+d≦0.9, and 1.8≦e≦2.2, and b+c+d=1). By replacing part of thenickel of this lithium nickel composite oxide with a metal,particularly, Cu or Fe, it is possible to suppress change in the crystalstructure, and to improve the discharge capacity and thermal stabilityof the secondary battery.

However, normally, unreacted lithium salts such as lithium carbonate,lithium nitrate and the like remain as impurities inside the lithiumnickel composite oxide after formation. Therefore, when a secondarybattery that uses this kind of lithium nickel composite oxide as acathode active material is charged under high-temperature conditions,there is a possibility that the unreacted lithium salts will undergooxidative decomposition. In that case, the generated decomposition gasmay cause a problem of improper secondary battery dimensions or adecrease in the battery characteristics.

In the case of such problems, removing the lithium salts by washing theformed lithium nickel composite oxide with water and drying iseffective. For example, JP2011-034861 (A), JP2003-017054 (A) andJP2007-273108 (A) disclose manufacturing methods of a lithium nickelcomposite oxide having a washing process that, by optimizing the amountof water used in washing and the amount of washing time, removesimpurities such as lithium carbonate while suppressing the elution oflithium. In these manufacturing methods, after the washing process, itis necessary to perform heat treatment in an air atmosphere, non-carbonatmosphere, or vacuum atmosphere in order to remove the moisturecontent.

However, when heat treatment is performed in an air atmosphere, thelithium that exists on the surface of the lithium nickel composite oxidereacts with carbon in the air and becomes lithium carbonate, so it isnot possible to solve the problem described above. On the other hand,when heat treatment is performed in a non-carbon atmosphere, or in avacuum atmosphere, the generation of lithium carbonate is suppressed,however, part of the lithium that exists on the surface isproton-exchanged with the hydrogen ion in the washing solution, andresults in a state close to an oxynickel oxide (NiOOH) state, so aproblem occurs in that the electrical conductivity of the cathode activematerial that is obtained is impaired. Moreover, due to proton exchange,hydrogen is arranged in the site where the lithium was originallyarranged, so there is also a problem in that during charging anddischarging, the diffusion of lithium ions is obstructed, and thereaction resistance increases. Furthermore, due to washing with water,the strength of the cathode active material decreases, so a problemoccurs in that the cathode active material cracks due to rollingpressure that is applied while forming the electrode, and the particlesthat are generated due to that become obstacles, so it becomesimpossible to obtain a highly dense electrode.

In regard to this, JPH09-231963 (A) and JP2010-155775 (A) disclosetechnology in which after washing is performed under specifiedconditions, heat treatment is performed on the lithium nickel compositeoxide in an oxygen atmosphere and at a temperature of 400° C. orgreater. By performing heat treatment in an oxygen atmosphere in thisway, it becomes possible to stabilize the crystallinity of the particlesurfaces.

However, in the technology of the literature above, it is necessary toperform the washing of the lithium nickel composite oxide using purewater having mass that is two times or more than the mass of the lithiumnickel composite oxide. Therefore, there is a possibility that a problemwill occur in which the slurry concentration during washing becomesexcessively low, and as the impurities are removed from the lithiumnickel composite oxide, lithium is also extracted from inside theparticles, and thus a decrease in the battery capacity and an increasein cathode resistance will occur due to lithium deficiency. Moreover,after the heat treatment, the amount of lithium on the surface decreasesas compared to the amount of lithium inside the particles, so there is apossibility that a problem will occur in which the diffusion of lithiuminside the cathode active material will become impaired, and that theconductive paths will become insufficient.

PATENT LITERATURE

[Patent Literature 1] JPH05-242891 (A) [Patent Literature 2]JP2011-034861 (A) [Patent Literature 3] JP2003-017054 (A) [PatentLiterature 4] JP2007-273108 (A) [Patent Literature 5] JPH09-231963 (A)[Patent Literature 6] JP2010-155775 (A)

SUMMARY OF INVENTION Problem to be Solved by Invention

Taking the problems above into consideration, the object of the presentinvention is to provide a cathode active material for a non-aqueouselectrolyte secondary battery easily and at low cost, and that when usedas cathode material for a non-aqueous electrolyte secondary battery, notonly has excellent charging and discharging capacity and outputcharacteristics, but also has excellent particle strength and weatherresistance.

Means for Solving Problems

The manufacturing method of a cathode active material for a non-aqueouselectrolyte secondary battery of the present invention has steps of:forming a 500 g/L to 2000 g/L slurry by adding water to a powder of alithium nickel composite oxide that is represented by a general formula(A): Li_(z)Ni_(1-x-y)Co_(x)M_(y)O₂, where 0.10≦x≦0.20, 0≦y≦0.10,0.97≦z≦1.20, and M is at least one element that is selected from amongMn, V, Mg, Mo, Nb, Ti and Al; washing the slurry by mixing; filteringthe slurry; and performing heat treatment at a temperature of no lessthan 120° C. and no greater than 550° C., and preferably 120° C. orgreater but less than 400° C. in an oxygen atmosphere having an oxygenconcentration of 80% by volume or more.

Preferably, the temperature of the water that is used during washing is10° C. to 50° C.

Preferably, the rate of temperature rise during heat treatment is 2°C./min to 10° C./min, and the moisture content after heat treatment is0.2% by mass or less.

Moreover, the cathode active material for a non-aqueous electrolytesecondary battery of the present invention that is obtained by themanufacturing method above is a cathode active material that has alayered hexagonal lithium nickel composite oxide that is expressed by ageneral formula (B): Li_(z)Ni_(1-x-y)Co_(x)M_(y)O₂, where 0.10≦x≦0.20,0≦y≦0.10, 0.95≦z≦1.10, and M is at least one element that is selectedfrom among Mn, V, Mg, Mo, Nb, Ti and Al. The cathode active material ofthe present invention is such that a coating layer is formed on thesurface thereof, and the composition ratio of lithium with respect tometal(s) other than lithium of that coating layer is 1.50 to 2.30.Preferably, there is no lithium deficiency in the coating layer.

Preferably, the specific surface area of the cathode active material is0.2 g/m² to 2.0 g/m². Moreover, preferably the particle strength of thecathode active material is 42 MPa or more. Furthermore, preferably, themoisture content after cathode active material was exposed in an airatmosphere for 5 days is less than 1.1% by mass, and the total carbonamount is less than 0.6% by mass.

The non-aqueous electrolyte secondary battery of the present inventionis formed using the cathode active material for a non-aqueouselectrolyte secondary battery of the present invention described above.

Effect of Invention

With the present invention, when used as cathode material of anon-aqueous electrolyte secondary battery, it is possible to provide acathode active material for a non-aqueous electrolyte secondary batterythat has not only excellent charging and discharging capacity and outputcharacteristics, but also has excellent particle strength and weatherresistance. Moreover, by using this kind of cathode active material ascathode material, it is possible to provide a non-aqueous electrolytesecondary battery that has low cathode resistance, and high output.Furthermore, with the present invention, this kind of cathode activematerial can be easily produced on an industrial scale, so theindustrial value is very large.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a 2032-type coin battery that wasused for evaluation.

FIG. 2 is a drawing for explaining an equivalent circuit that was usedfor measurement and analysis in impedance evaluation.

MODES FOR CARRYING OUT INVENTION

The inventors of the present invention, in order to solve the problemsabove, diligently performed research of lithium nickel composite oxideand a non-aqueous electrolyte secondary battery that uses that lithiumnickel composite oxide as cathode active material. As a result, it wasfound that in the case of a cathode active material that is obtained bywashing a lithium nickel composite oxide and then performing heattreatment in an oxygen atmosphere and at a specified temperature afterthe lithium carbonate and lithium nitrate on the surface of the lithiumnickel composite oxide have been removed, the lithium on the surfacethat became deficient during washing is supplemented from the inside ofthe particles, resintering of the surface proceeds, and a coating layeris formed. It was also found that such a cathode active material notonly has high particle strength due to the existence of the coatinglayer on the surface, but also has high resistance to weather(characteristic of not easily undergoing a change in quality due toatmospheric gases or carbon dioxide gas). Moreover, it was found thatthis cathode active material does not have lithium deficiency on thesurface thereof, so when using this cathode active material to form anon-aqueous electrolyte secondary battery, it is possible to reduce thecathode resistance of the secondary battery and to improve the outputcharacteristics. The present invention was invented based on thesefindings.

The details of the present invention is explained hereinafter bydividing it into three sections of (1) Manufacturing Method for CathodeActive Material for Non-Aqueous Electrolyte Secondary Battery, (2)Cathode Active Material for Non-aqueous Electrolyte Secondary Battery,and (3) Non-aqueous Electrolyte Secondary Battery

(1) Manufacturing Method for Cathode Active Material for Non-AqueousElectrolyte Secondary Battery

The manufacturing method for a cathode active material for a non-aqueouselectrolyte secondary battery of the present invention has a process offorming a 500 g/L to 2000 g/L slurry by adding water to a powder of alithium nickel composite oxide that is expressed by the general formula(A): Li_(z)Ni_(1-x-y)Co_(x)M_(y)O₂ (where 0.10≦x≦0.20, 0≦y≦0.10,0.97≦z≦1.20, and M is at least one element that is selected from amongMn, V, Mg, Mo, Nb, Ti and Al), then washing lithium nickel compositeoxide by stirring the slurry, and after filtering, performing heattreatment in an oxygen atmosphere having an oxygen content of 80% byvolume or more, and at a temperature of no less than 120° C. and nogreater than 550° C.

(1-a) Base Material [Composition]

The cathode active material that is obtained according to the presentinvention is expressed by the general formula (B):Li_(z)Ni_(1-x-y)Co_(x)M_(y)O₂ (where 0.10≦x≦0.20, 0≦y≦0.10, 0.95≦z≦1.10,and M is at least one element that is selected from among Mn, V, Mg, Mo,Nb, Ti and Al). However, depending on the conditions during washing,lithium (Li) may elute in the wash water, so in that case, it isnecessary to use a lithium nickel composite oxide that is expressed bythe general formula (A) above.

In other words, lithium nickel composite oxide having a lithium contentthat is the same or a little more than the target cathode activematerial is used as the base material. More specifically, lithium nickelcomposite oxide that in the general formula (A), the value of z thatexpresses the lithium content is 0.97 to 1.20, and preferably 0.98 to1.15, and even more preferably 1.00 to 1.08 is used. When the value of zis less than 0.97, the cathode resistance of the non-aqueous electrolytesecondary battery that uses the obtained cathode active material becomeslarge, and thus it is not possible to sufficiently improve the outputcharacteristics. On the other hand, when the value of z is greater than1.20, not only does the initial discharge capacity of the cathode activematerial decrease, the cathode resistance similarly becomes large.

[Particle Structure]

The structure of the lithium nickel composite oxide of the basematerial, from the aspect of increasing the contact surface area withthe electrolyte, is preferably in the form of secondary particles thatare formed by an aggregation of plural primary particles of a lithiumnickel composite oxide that is represented by the general formula (A).Particularly, from the aspect of forming secondary particles having gapsand boundaries into which electrolyte can penetrate, preferablysecondary particles that are formed by an aggregation of plural plateshaped and/or needle shaped primary particles are used.

[Average Particle Size]

The average particle size of the lithium nickel composite oxide basematerial is preferably controlled to be within the range 3 μm to 30 μm,and more preferably within the range 5 μm to 20 μm. By using a lithiumnickel composite oxide having such an average particle size as the basematerial, it is possible to improve the packing density of the obtainedcathode active material, and it is possible to increase the number ofcontact points between the cathode active material, and thus it ispossible to further improve the output characteristics and batterycapacity. In this specification, as the average particle size of thelithium nickel composite oxide, the mean volume diameter thereof is usedthat can be calculated, for example, from the volume integrated averagevalue measured using the laser diffraction scattering method.

[Specific Surface Area]

The specific surface area of the lithium nickel composite oxide of thebase material is basically passed on to the specific surface area of thecathode active material that is obtained with this lithium nickelcomposite oxide as a precursor. Therefore, as the lithium nickelcomposite oxide of the base material, preferably a lithium nickelcomposite oxide that has a specific surface area within the range of 0.2g/m² to 2.0 g/m², and more preferably within the range 0.2 g/m² to 1.8g/m², and even more preferably within the range 0.2 g/m² to 1.6 g/m² isused. As a result, it is possible to easily control the specific surfacearea of the cathode active material that is obtained within a suitablerange. The specific surface area can be measured by the BET method usingnitrogen gas adsorption.

(1-b) Washing Process

The washing process is a process for removing impurities such as lithiumcarbonate and lithium sulfate that exist on the surface of the lithiumnickel composite oxide by dispersing powder of lithium nickel compositeoxide in water to form a slurry, and stirring the slurry.

During this kind of washing process, particles that exist on the surfaceof the lithium nickel composite oxide are peeled away, however, bystirring during the washing process, particles adhere again to thesurface and cover the lithium nickel composite oxide. To explain this inmore detail, when the washed lithium nickel composite oxide is composedof primary particles, the lithium nickel composite oxide that exist onor near the surface of the primary particles is peeled away in the shapeof minute particles, and then adhere to the surface again and cover thesurface of the primary particles. Moreover, when washed lithium nickelcomposite oxide is composed of secondary particles, the primaryparticles on the surface are peeled away and adhere again to the surfaceto cover the surface of the secondary particles.

In the washing process, part of the lithium is eluted from the surfaceof the lithium nickel composite oxide, and a small amount of lithiumdeficiency occurs, however, by performing a heat-treatment process aswill be described later, the deficient lithium will be supplemented fromthe inside of the crystal.

[Slurry Concentration]

The slurry concentration when washing the lithium nickel composite oxideis 500 g/L to 2000 g/L, and preferably 600 g/L to 1800 g/L, and morepreferably 700 g/L to 1500 g/L. When the slurry concentration is lessthan 500 g/L, the amount of lithium that is eluted from the lithiumnickel composite oxide increases, and desorption of the lithium from thecrystal lattice of the lithium nickel composite oxide becomes excessive,so it becomes easy for the crystal structure to break apart. Moreover,the aqueous solution having a high pH absorbs the carbon dioxide gas inthe atmosphere, so it becomes easy for lithium carbonate to precipitateout. On the other hand, when the slurry concentration is greater than2000 g/L, the viscosity of the slurry become extremely high, so stirringbecomes difficult. Moreover, the alkali concentration in the slurrybecomes high, and the rate of dissolution of adhering matter on thesurface of the cathode active material becomes slow due to equilibrium,and so solid-liquid separation also becomes difficult.

[Water Temperature]

The temperature of the water used in the washing process is preferably10° C. to 50° C., and more preferably 15° C. to 40° C., and even morepreferably 20° C. to 30° C. When the water temperature is less than 10°C., it may not be possible to sufficiently remove the impurities. On theother hand, when the water temperature is greater than 50° C., theamount of eluted lithium increases, so the characteristics of thenon-aqueous electrolyte battery that is obtained may decrease.

The water that is used in the washing process is not particularlylimited, however, from the aspect of preventing a decrease in thebattery characteristics due to impurities adhering to the cathode activematerial, preferably pure water is used. Particularly, using pure waterhaving electrical conductivity of less than 10 μS/cm is preferred, andusing pure water having electrical conductivity of 1 μS/cm or less ismore preferred.

[Average Particle Size of Primary Particles]

During washing, the average particle size of minute particle shapedlithium nickel composite oxide that is peeled away from the surface ofprimary particles, and the average particle size of primary particlesthat are peeled away from the surface of secondary particles (hereafter,these will simply be referred to as “minute particles”) is preferably 1nm to 100 nm, and more preferably 5 nm to 50 nm. When the averageparticle size of the minute particles is less than 1 nm, the fineparticles may not have sufficient lithium-ion conductivity. On the otherhand, when the average particle size of minute particles is greater than100 nm, it becomes difficult to uniformly cover the surface lithiumnickel composite oxide, and therefore the uniform coating layer is notformed, thus there is a possibility that sufficient effect for reducingthe reaction resistance is not obtained. In this specification, also asthe average particle size of the minute particles, the mean volumediameter thereof is used that can be calculated for example, from thevolume integrated average value measured using the laser diffractionscattering method.

[Filtration]

Filtration that is performed after the washing process is notparticularly limited and it is possible to use any known method. As thefiltration method, it is possible to use a method that uses a filterpress, Nutsche (Buchner funnel) or the like.

(1-c) Heat-Treatment Process

The heat-treatment process is a process of heat treating the lithiumnickel composite oxide under specified conditions after washing andfiltering. Particularly, in the present invention, this heat-treatmentprocess is performed in an atmosphere having an oxygen content of 80% byvolume or more, and at a temperature of no less than 120° C. and no morethan 550° C.

By performing this kind of heat treatment, lithium that exists insidethe lithium nickel composite oxide is dispersed, the lithium deficiencyon the surface is supplemented, and resintering proceeds. As a result, acoating layer having a high concentration of lithium is formed, so it ispossible to improve the particle strength and weather resistance.Moreover, when making a non-aqueous electrolyte secondary battery thatuses this lithium nickel composite oxide as cathode active material, alithium-ion conduction path is formed at the boundary surface betweenthe cathode active material and the electrolyte, so it is possible toreduce the reaction resistance and improve the output characteristics ofthe battery.

In the present invention, the heat-treatment method is not particularlylimited, and it is possible to use a known method. However, from theaspect of forming a uniform coating layer on the lithium nickelcomposite oxide, preferably an electric furnace is used.

[Heat-Treatment Atmosphere]

The atmosphere during the heat-treatment process is an oxygen atmospherehaving an oxygen concentration of 80% by volume or greater, andpreferably 90% by volume or greater, and more preferably 100% by volume.When the oxygen concentration is less than 80% by volume, not only doesthe crystal structure break apart due to cationic mixing, but there isalso a possibility that the supplementation of lithium to sites wherethere is lithium deficiency will not be performed sufficiently.

[Heat-Treatment Temperature]

The heat-treatment temperature is not less than 120° C. and not morethan 550° C., and is preferably 120° C. or greater but less than 400°C., and more preferably 200° C. or greater but less than 350° C. Whenthe heat-treatment temperature is less than 120° C., a long amount oftime is required for heat treatment, and the resintering of the particlesurfaces does not proceed sufficiently, so it becomes difficult to forma coating layer that includes a high concentration of lithium. On theother hand, when the heat-treatment temperature is greater than 400° C.,the thickness of the coating layer that is formed by sintering becomes100 nm or greater, and even though the particle strength and the weatherresistance is improved, in the charging state, it become easy for thecrystal structure to break apart. Particularly, when the heat-treatmenttemperature is greater than 550° C., this tendency increases, and thebattery characteristics decrease due to the breaking apart of thecrystal structure.

[Rate of Temperature Rise]

The rate of temperature rise during heat treatment is preferably 2°C./min to 10° C./min, and more preferably 4° C./min to 6° C./min. Byregulating the rate of temperature rise during heat treatment to such arange, it is possible to suppress the occurrence of oxyhydroxides due tothe reaction between the moisture remaining inside the lithium nickelcomposite oxide and the lithium on the surface of the lithium nickelcomposite oxide, so it becomes possible to prevent a decrease in theelectrical conductivity of the obtained lithium nickel composite oxide.When the rate of temperature increase is less than 2° C./min, there is apossibility of a worsening of productivity due to the amount of timerequired for heat treatment. On the other hand, when the rate oftemperature increase is greater than 10° C./min, not only is it notpossible to avoid the problem above, but there is also a possible ofirregularity in the coating layer.

[Processing Time]

The processing time in the heat-treatment process is appropriatelyadjusted according to the amount of lithium nickel composite oxide beingprocessed and the performance of the apparatus being used, and is notparticularly limited. However, as will be described later, the moisturecontent of the cathode active material is preferably adjusted to be 0.2%by mass or less, and more preferably adjusted to be 0.1% by mass orless, and even more preferably adjusted to be 0.05% by mass or less.

(2) Cathode Active Material for Non-Aqueous Electrolyte SecondaryBattery

The cathode active material for a non-aqueous electrolyte secondarybattery of the present invention is formed using a layered hexagonallithium nickel composite oxide that is expressed by the general formula(B): Li_(z)Ni_(1-x-y)Co_(x)M_(y)O₂ (where 0.10≦x≦0.20, 0≦y≦0.10,0.95≦z≦1.10, and M is at least one element that is selected from amongMn, V, Mg, Mo, Nb, Ti and Al). A coating layer that includes a highconcentration of lithium is formed on the surface of this cathode activematerial, and the composition ratio (Li/Me) of lithium (Li) with respectto the metals other than lithium (Me=Ni, Co, Mn, V and the like) of thiscoating layer is 1.50 to 2.30.

This kind of cathode active material is obtained by the manufacturingmethod described above, and there is no lithium deficiency in thecoating layer of the surface thereof. Therefore, when making anon-aqueous electrolyte secondary battery that uses this cathode activematerial, it is possible to improve the initial discharge capacity andoutput characteristics of the battery. Moreover, due to the coatinglayer, this cathode active material has high particle strength and goodweather resistance, and it is possible to maintain the batterycharacteristics over a long period of time.

(2-a) Composition

The value z that expresses the composition ratio of lithium (Li) iscontrolled to be within the range 0.95 to 1.10, and preferably 0.98 to1.10, and more preferably 1.00 to 1.08. When the value of z is less than0.95, the reaction resistance of the cathode in the non-aqueouselectrolyte secondary battery becomes large, and it is not possible toimprove the output characteristics. On the other hand, when the value ofz is greater than 1.10, the initial discharge capacity of thenon-aqueous electrolyte secondary battery decreases.

However, in the coating layer, the composition ratio (Li/Me) of lithiumwith respect to the metal other than lithium must be controlled to bewith in the range 1.50 to 2.30, and preferably 1.60 to 2.20 and evenmore preferably 1.80 to 2.00. When the value of the ratio Li/Me is lessthan 1.50, not only does lithium deficiency occur on the surface of thecathode active material, but hydrogen is arranged in sites where lithiumshould be arranged, so the lithium-ion conduction paths are impaired,the reaction resistance increases, and there is a possibility thatsufficient output characteristics will not be obtained. On the otherhand, when the value of the ratio Li/Me is greater than 2.30, there is apossibility to occur a problem such as reduction of charge and dischargeefficiency.

Cobalt (Co) is an added element that contributes to the improvement ofthe cycling characteristic. The value x that expresses the compositionratio of cobalt is controlled to be within the range 0.10 to 0.20, andpreferably 0.13 to 0.17. When the value of x is less than 0.10, it isnot possible to obtain a sufficient cycling characteristic, and thecapacity retention greatly decreases. On the other hand, when the valuex is greater than 0.20, the initial discharge capacity is significantlyreduced.

Moreover, the cathode active material of the present invention can alsoinclude added elements (M) according to other uses. As a result, it ispossible to improve the durability and cycling characteristic of theobtained non-aqueous electrolyte secondary battery.

As the added element (M), it is possible to use at least one elementselected from among manganese (Mn), vanadium (V), magnesium (Mg),molybdenum (Mo), niobium (Nb), titanium (Ti) and aluminum (Al). Theseadded elements (M) are appropriately selected according to theperformance required for the secondary battery that uses the obtainedcathode active material.

The value y that indicates the amount of added element (M) included is0.10 or less and preferably 0.06 or less. When the value of y is greaterthan 0.10, the metal elements that contribute to the Redox reactiondecrease, so the battery capacity decreases.

The composition ratio described above can be measured by quantitativeanalysis or semi-quantitative analysis, and more specifically, can bemeasured by an X-ray photoelectron spectroscopy method or the like.

(2-b) Particle Structure

The cathode active material of the present invention includes a highconcentration of lithium on the surface thereof, and is characterized bycomprising a coating layer that has no lithium deficiency. Due to theexistence of this coating layer, it is possible to dramatically improvethe particle strength and the weather resistance. Moreover, when makinga non-aqueous electrolyte secondary battery that uses this cathodeactive material, it is possible to greatly improve the initial dischargeamount and the output characteristics. Whether or not there is lithiumdeficiency in the coating layer can be checked by X-ray photoelectronspectroscopy.

The thickness of this coating layer is preferably controlled to bewithin the range of 1 nm to 100 nm, and more preferably 5 nm to 50 nm,and even more preferably 10 nm to 30 nm. When the thickness of thecoating layer is less than 1 nm, it is not possible to sufficientlyimprove the particle strength and the weather resistance. On the otherhand, when the thickness is greater than 100 nm, a problem occurs inthat in the charged state, it becomes easy for the crystal structure tobreak apart, and there is a possibility that the battery characteristicswill decrease. The thickness of the coating layer can be determined witha cross-section observation of the cathode active material using ascanning electron microscope (SEM) in a state that the cathode activematerial is embedded in a resin and then is ready to be observed using across-section polisher processing or the like. More specifically, thethickness can be determined by measuring the thickness of the coatinglayer at 30 or more locations using SEM observation, and calculating theaverage value.

The cathode active material of the present invention can also compriseprimary particles of the lithium nickel composite oxide that isrepresented by the general formula (B) above, and/or secondary particlesthat are formed by an aggregation of these primary particles. However,from the aspect of improving the output characteristics by increasingthe contact surface area with the electrolyte, preferably the cathodeactive material comprises secondary particles, and particularly it ispreferred that the cathode active material comprise secondary particlesthat have gaps or grain boundaries in which electrolyte can penetrate.The structure of the cathode active material can be checked by SEMobservation of the cross section of the cathode active material.

(2-c) Average Particle Size

The average particle size of the cathode active material is preferablywithin the range 3 μm to 30 μm, and more preferably within the range 5μm to 20 μm. Cathode active material having an average particle sizethat is within the range above has high packing density, and thus it ispossible to further improve the characteristics such as battery capacityof the secondary battery that uses this cathode material. In thisspecification, also as the average particle size of the cathode activematerial, the mean volume diameter thereof is used that can becalculated, for example, from the volume integrated average valuemeasured using the laser diffraction scattering method.

(2-d) Moisture Content

After the heat-treatment process, the ratio of the mass of the moisturethat is included in the cathode active material with respect to thetotal mass of the cathode active material (hereafter, referred to as the“moisture content”) is preferably 0.2% by mass or less, and morepreferably 0.1% by mass or less, and even more preferably, 0.05% bymass. When the moisture content of the cathode active material isgreater than 0.2% by mass, the moisture absorbs the gas component,including the carbon and sulfur in the air, and there is a possibilitythat a lithium compound will be generated on the surface of the cathodeactive material.

Measurement of the moisture content is not particularly limited, and canbe performed using known methods. As such a method, for example, it ispossible to measure the moisture content by using a Karl Fischermoisture titrate, or the like.

(2-e) Specific Surface Area

The specific surface area of the cathode active material after theheat-treatment process is preferably controlled to be 0.2 g/m² to 2.0g/m², and more preferably 0.2 g/m² to 1.8 g/m², and even more preferably0.2 g/m² to 1.6 g/m². When the specific surface area is less than 0.2g/m², the cathode resistance increases, and it is not possible toimprove the output characteristics. On the other hand, when the specificsurface area is greater than 2.0 g/m², the amount of heat generated dueto reaction with the electrolyte suddenly increases, and there is apossibility that the thermal stability will decrease. The specificsurface area can be measured by the BET method using nitrogen gasadsorption.

(2-f) Particle Strength

The cathode active material of the present invention preferably hasparticle strength of 42 MPa or greater, and more preferably particlestrength of 54 MPa or greater, and even more preferably particlestrength of 57 MPa or greater. When the particle strength is less than42 MPa, the cathode active material deforms or breaks when being rolledto form the electrode, so there is a possibility that a highly denseelectrode cannot be formed. The particle strength can be measured by amicro-compression tester.

(2-g) Weather Resistance

The cathode active material of the present invention preferably has amoisture content of less than 1.1% by mass, and more preferably 0.9% bymass or less, and even more preferably 0.7% by mass or less after 5 daysof exposure in an air atmosphere. Moreover, preferably the total carbonamount (total carbon content) is less than 0.6% by mass, and morepreferably 0.5% by mass or less, or even more preferably 0.4% by mass orless. Cathode active material having a moisture content and total carbonamount within such ranges has excellent weather resistance and does noteasily change due to gas in the atmosphere, so it is possible to makethe storage ability of the obtained non-aqueous electrolyte secondarybattery high. The moisture content can be measured by a Karl Fischermoisture titrate, and the total carbon amount can be measured by a totalorganic carbon analyzer.

(3) Non-Aqueous Electrolyte Secondary Battery

The non-aqueous electrolyte secondary battery of the present inventionhas a cathode, an anode, a separator and non-aqueous electrolyte, andthe cathode active material of the present invention is used as thecathode material for the cathode.

In the following, the non-aqueous electrolyte secondary battery of thepresent invention will be explained. However, the embodiment explainedbelow is only an example, and it is possible for the non-aqueouselectrolyte secondary battery of the present invention to undergovarious changes or improvements based on the embodiments disclosed inthis specification and based on the knowledge of one skilled in the art.Moreover, in the explanation below, the use of the non-aqueouselectrolyte secondary battery of the present invention is notparticularly limited.

(3-a) Cathode

First, the cathode, which is a feature of the secondary battery of thepresent invention, will be explained.

The cathode of the non-aqueous electrolyte secondary battery is made asdescribed below using the cathode active material for a non-aqueouselectrolyte secondary battery that is obtained according to the presentinvention.

First, a cathode paste is made by mixing a conductive material andbonding agent with powdered cathode active material that was obtainedaccording to the present invention, and then kneading this mixture. Therespective mixture ratios in the cathode paste at this time are alsoimportant elements for determining the performance of the non-aqueouselectrolyte secondary battery. When the solid portion of the cathodematerial without the solvent is taken to be 100 parts by mass, then, asin the case of a general cathode of a non-aqueous electrolyte secondarybattery, the amount of cathode active material that is included is takento be 60 parts by mass to 95 parts by mass, the amount of conductivematerial that is ided is taken to be 1 part by mass to 20 parts by mass,and the amount of bonding agent included is taken to be 1 part by massto 20 parts by mass.

The obtained cathode paste is applied, for example, on the surface of analuminum foil current collector, and then dried to cause the solvent todissipate. When necessary, it is possible to apply pressure with a rollpress to increase the electrode density. In this way, it is possible tomake a sheet-shaped cathode. A sheet-shaped cathode can be provided formaking a battery by cutting the cathode to a size suitable for thetarget battery. However, manufacturing the cathode is not limited tothis kind of method, and it is possible to manufacture the cathode bysome other method.

When manufacturing the cathode, it is possible to use graphite (naturalgraphite, artificial graphite, expanded graphite, and the like), or acarbon black material such as acetylene black, Ketjenblack and the likeas the conductive material.

Moreover, it is possible to use polyvinylidene fluoride (PVDF),polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene dienerubber, styrene butadiene, cellulose resin, polyacrylic acid and thelike as the bonding agent.

When necessary, it is also possible to add a solvent for dissolving thecathode active material, the conductive material and the bonding agent.It is possible to use, for example, an organic solvent such asN-methyl-2-pyrrolidone and the like as the solvent. Furthermore, it isalso possible to add activated carbon in order to increase the electricdouble-layer capacity.

(3-b) Anode

For the anode, it is possible to use an anode that is formed by mixing abinding agent with metal lithium, lithium alloy or the like, or with ananode active material for which adsorption or desorption of lithium ionsis possible, adding a suitable solvent to form a paste-like anodematerial, applying that anode material onto the surface of a metal foil,for example copper foil current collector, drying and when necessary,applying pressure to increase the electrode density.

As the anode active material, it is possible to use an organic compoundsintered body such as natural graphite, artificial graphite, phenolresin and the like, or powdered carbon material such as coke. In thiscase, as the anode binding agent, as in the case of the cathode, it ispossible to use a fluororesin that includes PVDF and the like, and asthe solvent for dispersing the active material and the binding agent, itis possible to use an organic solvent such as N-methyl-2-pyrrolidone andthe like.

(3-c) Separator

The separator is arranged so as to be held between the cathode and theanode, and has the function of separating the cathode and the anode andmaintaining the electrolyte. As such a separator, it is possible to use,for example, a thin film of polyethylene, polypropylene and the like,having many fine holes, however, the separator is not particularlylimited as long as it has the functions described above.

(3-d) Non-Aqueous Electrolyte

The non-aqueous electrolyte is formed by dissolving lithium salt as asupporting salt into an organic solvent.

As the organic solvent, it is possible to use a single kind or a mixtureof two or more kinds selected from: a cyclic carbonate such as ethylenecarbonate, propylene carbonate, butylene carbonate, trifluoro propylenecarbonate and the like; a chain carbonate such as diethyl carbonate,dimethyl carbonate, ethyl methyl carbonate, dipropyl carbonate and thelike; an ether compound such as tetrahydrofuran,2-methyltetrahydrofuran, dimethoxyethane and the like; a sulfur compoundsuch as ethyl methyl sulfone, butane sultone and the like; and aphosphorus compound such as triethyl phosphate, trioctyl phosphate andthe like.

As the supporting salt, it is possible to use LiPF₆, LiBF₄, LiClO₄,LiAsF₆, LiN(CF₃SO₂)₂ and the like, or a composite of these.

Furthermore, the non-aqueous electrolyte can also include a radicalscavenger, a surfactant, a flame retardant and the like.

(3-e) Battery Shape and Construction

Various shapes such as a cylindrical shape or layered shape can be usedas the shape of the non-aqueous electrolyte secondary battery of thepresent invention that is formed using the cathode, anode, separator andnon-aqueous electrolyte explained above.

No matter what shape is used, electrodes are formed by layering thecathode and anode by way of the separator, and the electrodes are thenimpregnated with the non-aqueous electrolyte, then collector leads orthe like are used to connect between the cathode collector and a cathodeterminal that goes to the outside, and between the anode collector andan anode terminal that goes to the outside; this is then sealed in abattery case to complete the non-aqueous electrolyte secondary battery.

(3-f) Characteristics

The non-aqueous electrolyte secondary battery of the present inventionis constructed as described above and has a cathode that uses thecathode active material of the present invention, so it is possible toachieve high initial discharge capacity and low cathode resistance. Forexample, in the case of constructing a 2032 type coin battery such asillustrated in FIG. 1 using the cathode active material of the presentinvention, it is possible to achieve an initial discharge capacity of190 mAh/g or more, and preferably 195 mAh/g or more, and even morepreferably 197 mAh/g or more. Moreover, it is possible to achieve acathode resistance of 5.5Ω or less, and preferably 5.0Ω or less, andeven more preferably 4.3Ω or less. Furthermore, the cathode activematerial of the present invention has high particle strength, andexcellent weather resistance, so the non-aqueous electrolyte secondarybattery that uses this cathode active material is capable of maintainingthe battery characteristics over a long period of time.

EXAMPLES

In the following, the present invention will be explained in detailusing examples and comparative examples. However, it should beunderstood that the present invention is not limited to the specificdetails of these examples and comparative examples. In the example andcomparative examples below, unless stated otherwise, samples usingspecial grade chemicals manufactured by Wako Pure Chemical IndustriesCo., Ltd. were used for manufacturing the lithium nickel compositeoxide, the cathode active material and the secondary battery.

Example 1

Lithium nickel composite oxide powder that is represented by the generalformula; Li_(1.06)Ni_(0.82)Co_(0.15)Al_(0.03)O₂ that was obtained bymixing oxide powder having nickel as the main component and lithiumhydroxide and then sintering the resultant mixture, was used as the basematerial of the cathode active material. This lithium nickel compositeoxide powder comprised lithium nickel composite oxide that wasrepresented by the general formula above, and comprised secondaryparticles that were formed by an aggregation of plural plate shapedand/or needle shaped primary particles having an average particle sizeof 0.3 μm. Moreover, the average particle size of this lithium nickelcomposite oxide powder was 12.0 μm, and the specific surface area was1.2 m²/g. The construction of this lithium nickel composite oxide wasobserved by SEM (JSM-6360LA, manufactured by JEOL Ltd.), the averageparticle size was measured using the volume integrated average value inthe laser diffraction scattering method, and the specific surface areawas measured by the BET method using nitrogen gas adsorption.

A slurry was formed by adding pure water having electric conductivity of5 μS/cm (temperature: 22° C.) to the lithium nickel composite oxide, theslurry was washed by stirring for 30 minutes, after which the slurry wasfiltered using a Nutsche. The slurry concentration at this time was 1500g/L. Moreover, the surface of the lithium nickel composite oxide at thistime was observed by SEM, and as a result, it was confirmed that therewere minute particles having an average particle size of 30 nm on thesurface.

After that, heat treatment was performed by using a muffle furnace(PVF-3060, manufactured by Hirochiku Co., Ltd.) was used in an oxygenatmosphere having an oxygen concentration of 100% by volume to raise thetemperature to 210° C. at a rate of temperature increase of 5° C./min,and that temperature was maintained until the moisture content became0.05% by mass. At this time, the processing time from the start oftemperature rising to the end of temperature keeping at the abovetemperature was 14 hours.

[Characteristics of Cathode Active Material]

The characteristics of the obtained cathode active material wereconfirmed to be as described below.

a) Composition

As a result of measurement using an X-ray diffractometer (Multi Flex,manufactured by Rigaku Corp.), it was confirmed that the cathode activematerial that was obtained in this way was a layered hexagonal lithiumnickel composite oxide that is represented by the general formulaLi_(1.06)Ni_(0.82)Co_(0.15)Al_(0.03)O₂.

b) Particle Structure

After the cathode active material was embedded in resin and thenperforming a cross-section polishing process on it, the cathode activematerial was observed by SEM observation. As a result, this cathodeactive material was confirmed to comprise secondary particles that areformed by an aggregation of plural primary particles. Moreover, thecoating layer was observed by X-ray photoelectron spectroscopymeasurement, and as a result it was confirmed that there was no lithiumdeficiency, and that Li/Me was 2.00.

c) Average Particle Size and Specific Surface Area

By performing measurement using a laser scattering type particle sizeanalyzer (manufactured by Nikkiso Co., Ltd.), it was confirmed that theaverage particle size of this cathode active material was 12 μm.Moreover, as a result of measurement using the BET method by nitrogengas adsorption, it was confirmed that the specific surface area of thiscathode active material was 0.9 m²/g.

[Evaluation of Cathode Active Material]

The a) particle strength and b) weather resistance of the obtainedcathode active material were evaluated as described below.

a) Particle Strength

By performing measurement using a micro-compression tester (MCT Wseries, manufactured by Shimadzu Corporation), it was confirmed that theparticle strength of this cathode active material was 60 MPa.

In Examples 2 to 15 and Comparative Examples 1 to 7, the particlestrength in Example 1 was taken to be 100, and with this value as astandard, it was determined that when the relative value was less than70 (particle strength of less then 42 MPa) the strength wasinsufficient.

b) Weather Resistance Test

After the cathode active material had been exposed in an air atmospherefor 5 days, a sample was taken, and evaluated by measuring the moisturecontent and the total carbon amount (overall carbon content) at thattime. The moisture content was measured with a Karl Fischer moisturemeter (CA-100, manufactured by Mitsubishi Chemical Corporation), and thetotal carbon amount was measured by high-frequency combustion infraredanalysis (CS-600, manufactured by LECO Japan Corporation). As a result,it was found that the moisture content of Example 1 was 0.7% by mass,and the total carbon amount was 0.4% by mass.

In Examples 2 to 15 and Comparative Examples 1 to 7 described below, thevalues for the moisture content and total carbon amount in Example 1 aretaken to be 100, and with these values as standards, it was determinedthat when relative values are 150 or more (moisture content of 1.1% bymass or greater, or a total carbon amount of 0.6% by mass or greater)the weather resistance has decreased.

[Manufacture of Non-Aqueous Electrolyte Secondary Battery]

Next, a coin battery 1 as illustrated in FIG. 1 was manufactured usingthe obtained cathode active material, and the characteristics wereevaluated.

This coin battery 1 comprises a case 2, and electrode 3 that is housedinside this case 2.

The case 2 has a cathode can 2 a that is hollow and that is opened onone end, and an anode can 2 b that is arranged in the opening section ofthis cathode can 2 a, and is constructed so that when the anode can 2 bis arranged in the opening section of the cathode can 2 a, a space isformed between the anode can 2 b and the cathode can 2 a that houses theelectrode 3.

The electrode 3 comprises a cathode 3 a, a separator 3 c and an anode 3b, that are layered in that order, and housed in the case 2 so that thecathode 3 a comes in contact with the inner surface of the cathode can 2a, and the anode 3 b comes in contact with the inner surface of theanode can 2 b.

The case 2 comprises a gasket 2 c, and is secured by this gasket 2 c sothat the cathode 2 a and anode 2 b are maintained in an electricallyinsulated state. Moreover, the gasket 2 c has a function of sealing thegap between the cathode can 2 a and anode can 2 b so that the inside ofthe case 2 is sealed off from the outside so as to be airtight andfluid-tight.

The coin battery 1 was manufactured as described below. First, the 52.5mg of the obtained cathode active material was mixed with 15 mg ofacetylene black and 7.5 mg of polytetrafluoroethylene resin, thenpressed at a pressure of 100 MPa to form a cathode having an 11 mmdiameter and 100 μm thickness. This cathode 3 a was then dried in avacuum drier for 12 hours at 120° C. Using this cathode 3 a, anode 3 b,separator 3 c and electrolyte, a coin battery 1 was manufactured insidea glovebox in an Ar atmosphere, the dew point of which was controlled to−80° C.

An anode sheet that was formed by coating copper foil with graphitepowder and polyvinylidene fluoride and punched into a disk shape havinga 14 mm diameter was used as the anode 3 b. Moreover, porouspolyethylene film having a film thickness of 25 m was used as theseparator 3 c. 1 M of a mixed solution having equal parts of ethylenecarbonate (EC) and diethyl carbonate (DEC) and LiClO₄ as the supportingelectrolyte (manufactured by Tobmiyama Pure Chemical Industries, Ltd.)was used as the electrolyte.

[Evaluation of Electrical Characteristics]

The a) initial discharge capacity and b) cathode resistance of obtainedcoin battery 1 were evaluated as described below.

a) Initial Discharge Capacity

After making the coin battery 1, the coin battery 1 was left for 24hours, and after the open circuit voltage (OCV) became stable, the coinbattery 1 was charged to a cut-off voltage of 4.3 V with the currentdensity with respect to the cathode being 0.1 mA/cm², and after stoppingfor one hour, the coin battery 1 was discharged to a cut-off voltage of3.0 V and the capacity at that time was evaluated as being the initialdischarge capacity. As a result, it was found that the initial dischargecapacity of Example 1 was 198.8 mAh/g.

b) Cathode Resistance (Rct)

The coin battery 1 was charged to a charge potential of 4.1 V, and byusing a frequency response analyzer and a potentio-galvanostat (1255B,manufactured by Solatron) to measure the resistance value by analternating current impedance method, the Nyquist plot illustrated inFIG. 2 was obtained. This Nyquist plot is expressed as a sum ofcharacteristic curves that indicate the solvent resistance, anoderesistance and capacity, and cathode resistance and capacity, so thevalue of the cathode resistance was calculated by fitting calculationusing an equivalent circuit based on this Nyquist plot. As a result, thecathode resistance in Example 1 was 3.9Ω.

In Examples 2 to 15 and Comparative Examples 1 to 7 below, the value ofthe cathode resistance in Example 1 is taken to be 100, then with thisvalue as a standard, when the absolute value is greater than 141(cathode resistance exceeds 5.5Ω), it is determined that the cathoderesistance is high.

Example 2

Except for the slurry concentration during washing being 750 g/L, acathode active material was obtained in the same way as in Example 1.The characteristics of this cathode active material are shown inTable 1. Moreover, evaluation of this cathode active material and asecondary battery that was made using this cathode active material isshown in Table 2.

Example 3

Except for the heat-treatment temperature being 500° C., a cathodeactive material was obtained in the same way as in Example 1. Thecharacteristics of this cathode active material are shown in Table 1.Moreover, evaluation of this cathode active material and a secondarybattery that was made using this cathode active material is shown inTable 2.

Example 4

Except for the atmosphere during heat-treatment being an oxygenatmosphere with an oxygen concentration of 80% by mass, a cathode activematerial was obtained in the same way as in Example 1. Thecharacteristics of this cathode active material are shown in Table 1.Moreover, evaluation of this cathode active material and a secondarybattery that was made using this cathode active material is shown inTable 2.

Example 5

Except for the heat-treatment temperature being 120° C., a cathodeactive material was obtained in the same way as in Example 1. Thecharacteristics of this cathode active material are shown in Table 1.Moreover, evaluation of this cathode active material and a secondarybattery that was made using this cathode active material is shown inTable 2.

Example 6

Except for the heat-treatment temperature being 350° C., a cathodeactive material was obtained in the same way as in Example 1. Thecharacteristics of this cathode active material are shown in Table 1.Moreover, evaluation of this cathode active material and a secondarybattery that was made using this cathode active material is shown inTable 2.

Example 7

Except for the heat-treatment temperature being 420° C., a cathodeactive material was obtained in the same way as in Example 1. Thecharacteristics of this cathode active material are shown in Table 1.Moreover, evaluation of this cathode active material and a secondarybattery that was made using this cathode active material is shown inTable 2.

Example 8

Except for temperature during washing being 10° C., a cathode activematerial was obtained in the same way as in Example 1. Thecharacteristics of this cathode active material are shown in Table 1.Moreover, evaluation of this cathode active material and a secondarybattery that was made using this cathode active material is shown inTable 2.

Example 9

Except for temperature during washing being 50° C., a cathode activematerial was obtained in the same way as in Example 1. Thecharacteristics of this cathode active material are shown in Table 1.Moreover, evaluation of this cathode active material and a secondarybattery that was made using this cathode active material is shown inTable 2.

Example 10

Except for the rate of temperature rise during heat treatment being 2°C./min, a cathode active material was obtained in the same way as inExample 1. The characteristics of this cathode active material are shownin Table 1. Moreover, evaluation of this cathode active material and asecondary battery that was made using this cathode active material isshown in Table 2.

Example 11

Except for the rate of temperature rise during heat treatment being 10°C./min, a cathode active material was obtained in the same way as inExample 1. The characteristics of this cathode active material are shownin Table 1. Moreover, evaluation of this cathode active material and asecondary battery that was made using this cathode active material isshown in Table 2.

Example 12

Except for the temperature during washing being 8° C., a cathode activematerial was obtained in the same way as in Example 1. Thecharacteristics of this cathode active material are shown in Table 1.Moreover, evaluation of this cathode active material and a secondarybattery that was made using this cathode active material is shown inTable 2.

Example 13

Except for the temperature during washing being 55° C., a cathode activematerial was obtained in the same way as in Example 1. Thecharacteristics of this cathode active material are shown in Table 1.Moreover, evaluation of this cathode active material and a secondarybattery that was made using this cathode active material is shown inTable 2.

Example 14

Except for the rate of temperature rise during heat treatment being 1°C./min, a cathode active material was obtained in the same way as inExample 1. The characteristics of this cathode active material are shownin Table 1. Moreover, evaluation of this cathode active material and asecondary battery that was made using this cathode active material isshown in Table 2.

Example 15

Except for the rate of temperature rise during heat treatment being 12°C./min, a cathode active material was obtained in the same way as inExample 1. The characteristics of this cathode active material are shownin Table 1. Moreover, evaluation of this cathode active material and asecondary battery that was made using this cathode active material isshown in Table 2.

Comparative Example 1

Except for the slurry concentration during washing being 2500 g/L, acathode active material was obtained in the same way as in Example 1.The characteristics of this cathode active material are shown inTable 1. Moreover, evaluation of this cathode active material and asecondary battery that was made using this cathode active material isshown in Table 2.

Comparative Example 2

Except for the slurry concentration during washing being 400 g/L, acathode active material was obtained in the same way as in Example 1.The characteristics of this cathode active material are shown inTable 1. Moreover, evaluation of this cathode active material and asecondary battery that was made using this cathode active material isshown in Table 2.

Comparative Example 3

Except for the heat-treatment temperature being 100° C., a cathodeactive material was obtained in the same way as in Example 1. Thecharacteristics of this cathode active material are shown in Table 1.Moreover, evaluation of this cathode active material and a secondarybattery that was made using this cathode active material is shown inTable 2.

Comparative Example 4

Except for the heat-treatment temperature being 700° C., a cathodeactive material was obtained in the same way as in Example 1. Thecharacteristics of this cathode active material are shown in Table 1.Moreover, evaluation of this cathode active material and a secondarybattery that was made using this cathode active material is shown inTable 2.

Comparative Example 5

Except for the atmosphere during heat-treatment being an oxygenatmosphere with an oxygen concentration of 50% by mass, a cathode activematerial was obtained in the same way as in Example 1. Thecharacteristics of this cathode active material are shown in Table 1.Moreover, evaluation of this cathode active material and a secondarybattery that was made using this cathode active material is shown inTable 2.

Comparative Example 6

Except for the atmosphere during heat-treatment being an air atmosphere,a cathode active material was obtained in the same way as in Example 1.The characteristics of this cathode active material are shown inTable 1. Moreover, evaluation of this cathode active material and asecondary battery that was made using this cathode active material isshown in Table 2.

Comparative Example 7

Except for the atmosphere during heat-treatment being a vacuumatmosphere, a cathode active material was obtained in the same way as inExample 1. The characteristics of this cathode active material are shownin Table 1. Moreover, evaluation of this cathode active material and asecondary battery that was made using this cathode active material isshown in Table 2.

TABLE 1 Heat-treatment process Washing Process Tem- Slurry Average pera-Water con- particle ture Positive electrode active materialcharacteristics tem- cen- size of Tem- rising Specific Average Mois-pera- tra- minute pera- Atmos- rate Li surface particle ture ture tionparticles ture phere (° C./ Crystal defi- area size content (° C.) (g/L)(nm) (° C.) (0, %) min) General formula structure ciency Li/Me (m²/g)(μm) (%) Example-1 22 1600 30 210 100 5Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂ Layered NO 2.00 0.9 12 0.06Example-2 22 750 30 210 100 5 Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂Layered NO 1.90 1.3 12 0.05 Example-3 22 1500 50 500 100 5Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂ Layered NO 2.10 0.3 12.5 0.05Example-4 22 1500 32 210 60 5 Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂Layered NO 1.70 0.3 12 0.05 Example-5 22 1500 17 120 100 5Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂ Layered NO 1.90 1.5 12 0.05Example-6 22 1500 37 360 100 5 Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂Layered NO 2.10 0.6 12.3 0.05 Example-7 22 1500 48 420 100 5Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂ Layered NO 2.21 0.5 12.5 0.05Example-8 10 1500 31 210 100 5 Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂Layered NO 2.00 0.8 12 0.05 Example-9 80 1500 32 210 100 5Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂ Layered NO 1.60 1.4 12 0.06Example-10 22 1500 29 210 100 2 Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂Layered NO 2.00 0.8 12 0.06 Example-11 22 1500 30 210 100 10Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂ Layered NO 2.00 0.8 12 0.05Example-12 8 1500 28 210 100 5 Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂Layered NO 2.00 0.8 12 0.05 Example-13 55 1500 30 210 100 5Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂ Layered NO 1.50 1.8 12 0.06Example-14 22 1500 31 210 100 1 Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂Layered NO 2.00 0.9 12 0.06 Example-15 22 1500 30 210 100 12Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂ Layered NO 2.00 0.9 12 0.06Comparative 22 2900 34 210 100 5 Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂Layered NO 2.20 0.6 12 0.06 Example-1 Comparative 22 400 31 210 100 5Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂ Layered Yes 1.10 2.1 12 0.06Example-2 Comparative 22 1500 4 100 100 5Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂ Layered NO 1.20 1.6 12 0.06Example-3 Comparative 22 1500 70 700 100 5Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂ Layered Yes 1.40 0.1 13.2 0.06Example-4 Comparative 22 1500 29 210 50 5Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂ Layered NO 1.30 1.0 12 0.06Example-5 Comparative 22 1500 30 210 Air 5Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂ Layered NO 1.00 0.9 12 0.06Example-6 Comparative 22 1500 31 210 Vaccum 5Li_(1.05)Ni_(0.02)Co_(0.15)Al_(0.03)O₂ Layered NO 1.30 1.0 12 0.05Example-7

TABLE 2 Secondary battery Positive electrode Initial active materialdischarge Positive Particle Moisture Total capacity electrode strengthcontent carbon (mAh/g) resistance Example-1 100 100 100 198.8 100Example-2 99 99 95 199.2 110 Example-3 152 78 80 195.4 95 Example-4 9998 110 197.6 117 Example-5 72 112 108 194.2 109 Example-6 121 91 91196.3 98 Example-7 138 83 84 195.6 96 Example-8 100 99 97 198.5 92Example-9 99 98 96 198.0 105 Example-10 98 102 91 198.9 93 Example-11 9291 89 197.9 112 Example-12 95 102 106 196.2 102 Example-13 83 110 112192.1 141 Example-14 98 101 91 199.0 98 Example-15 110 113 128 193.4 109Comparative 100 98 103 185.2 105 Example-1 Comparative 50 189 192 186.6148 Example-2 Comparative 52 115 114 180.1 134 Example-3 Comparative 18460 50 166.0 165 Example-4 Comparative 100 110 105 188.8 152 Example-5Comparative 98 101 115 180.5 172 Example-6 Comparative 99 101 102 194.4155 Example-7

[Evaluation]

As can be clearly seen from Table 2, the cathode active materials inExamples 1 to 15 are manufactured according to the manufacturing methodof the present invention, so the particle strength is high and weatherresistance is excellent. Moreover, when using these cathode activematerials, a non-aqueous electrolyte secondary battery having a highinitial discharge capacity and low cathode resistance was obtained.

However, in the case of the secondary batteries that used the cathodeactive materials of Examples 12 to 15, the water temperature in thewashing process or the rate of temperature rise in the heat-treatmentprocess were not within the preferable ranges of the present invention,so when compared with the other examples, there were cases in which thefollowing problems occurred.

In Example 12, the water temperature during washing was lower and it wasnot possible to sufficiently remove impurities. Therefore, decompositiongas was generated due to unreacted lithium salt, and the batterydimensions were bad.

In Example 13, the water temperature during washing was high, and theamount of eluted lithium increased, so it was not possible tosufficiently improve the initial discharge amount or cathode resistance.

In Example 14, the rate of temperature rise during the heat-treatmentprocess was slow, so productivity worsened.

In Example 15, the rate of temperature rise during the heat-treatmentprocess was fast, so it was not possible to suppress the generation ofoxyhydroxides, and thus it was not possible to sufficiently improve theinitial discharge capacity. Moreover, the rate of temperature rise wasfast, so a sufficient coating layer could not be generated, and thetotal carbon amount increased a little.

On the other hand, the Comparative Examples 1 to 7 are examples in whichthe slurry concentration, and the temperature and atmosphere during heattreatment were outside the range of the present invention.

In Comparative Example 1, the particle strength, weather resistance andcathode resistance were all equivalent with those in Examples 1 to 15,however, due to the slurry concentration during washing being high, theviscosity of the slurry became very high, which essentially made itdifficult to perform production on an industrial scale. Moreover, theremoval of impurities such as lithium carbonate that adhered to thecathode active material was insufficient, and due to that, it was notpossible to sufficiently improve the initial discharge capacity.

In Comparative Example 2, the slurry concentration during washing waslow, the amount of eluted lithium during the washing process increased,and lithium deficiency occurred. Therefore, it became easy for thecrystal structure to break down, and the particle strength decreased.Moreover, as the lithium was eluted, the pH value of the water used inwashing became high, carbonized gas in the air was absorbed, and lithiumcarbonate precipitated out again, so weather resistance decreased.Furthermore, the initial discharge capacity and cathode resistance alsobecame worse.

In Comparative Example 3, the heat-treatment temperature was low, and along time was required for heat treatment of the cathode active materialafter washing, so a difference (gradient) occurred in the lithiumconcentration on the surface of the particles and inside the particles,and as a result, the capacity and resistance became worse.

In Comparative Example 4, even though the particle strength and theweather resistance were good, the initial discharge capacity and cathoderesistance became worse. This was probably due to the highheat-treatment temperature, and because transition metals were dissolvedin lithium sites in the layered structure of the cathode activematerial.

In Comparative Example 5 to 7, the atmosphere during heat treatment wasnot suitable, and there was not the necessary oxygen concentration forlithium migration, and lithium on the crystal surface of the lithiumnickel composite oxide was insufficient, so the cathode resistanceworsened.

INDUSTRIAL APPLICABILITY

The manufacturing method of a cathode active material for a non-aqueouselectrolyte secondary battery of the present invention was easy andsuitable for large-scale production, so has large industrial value.

Moreover, the non-aqueous electrolyte secondary battery of the presentinvention is suitable as the power supply for compact and mobileelectric devices (notebook personal computers, cell phones, and thelike) that require a very high capacity. Furthermore, the non-aqueouselectrolyte secondary battery of the present invention has excellentweather resistance, and can be made to be compact and have high output,so is also suitable as the power supply for transport equipment in whichinstallation space is limited. The present invention can also be used asa power supply for an electric vehicle that is purely driven by electricpower, as well as a power supply for a so-called hybrid automobile thatis used together with a combustion engine such as a gasoline engine ordiesel engine.

EXPLANATION OF REFERENCE NUMBERS

-   1 Coin battery-   2 Case-   2 a Cathode can-   2 b Anode can-   2 c Gasket-   3 Electrode-   3 a Cathode-   3 b Anode-   3 c Separator

1. A manufacturing method for manufacturing a cathode active materialfor a non-aqueous electrolyte secondary battery, comprising steps of:forming a 500 g/L to 2000 g/L slurry by adding water to a powder of alithium nickel composite oxide that is represented by a general formula(A): Li_(z)Ni_(1-x-y)Co_(x)M_(y)O₂, where 0.10≦x≦0.20, 0≦y≦0.10,0.97≦z≦1.20, and M is at least one element that is selected from amongMn, V, Mg, Mo, Nb, Ti and Al; washing the slurry by mixing; filteringthe slurry; and performing heat treatment at a temperature of no lessthan 120° C. and no greater than 550° C. in an oxygen atmosphere havingan oxygen concentration of 80% by volume or more.
 2. The manufacturingmethod for manufacturing a cathode active material for a non-aqueouselectrolyte secondary battery according to claim 1, wherein atemperature of the water that is used during the washing process is 10°C. to 50° C.
 3. The manufacturing method for manufacturing a cathodeactive material for a non-aqueous electrolyte secondary batteryaccording to claim 1, wherein the temperature during the heat treatmentis 120° C. or greater but less than 400° C.
 4. The manufacturing methodfor manufacturing a cathode active material for a non-aqueouselectrolyte secondary battery according to claim 1, wherein a rate oftemperature rise during the heat treatment is 2° C./min to 10° C./min.5. The manufacturing method for manufacturing a cathode active materialfor a non-aqueous electrolyte secondary battery according to claim 1,wherein a moisture content of the cathode active material after the heattreatment is 0.2% by mass or less.
 6. A cathode active material for anon-aqueous electrolyte secondary battery obtained by the manufacturingmethod according to claim 1 and comprising a layered hexagonal lithiumnickel composite oxide that is expressed by a general formula (B):Li_(z)Ni_(1-x-y)Co_(x)M_(y)O₂, where 0.10≦x≦0.20, 0≦y≦0.10, 0.95≦z≦1.10,and M is at least one element that is selected from among Mn, V, Mg, Mo,Nb, Ti and Al, with a coating layer formed on a surface of the cathodeactive material, and a composition ratio of lithium with respect tometal(s) other than lithium of the coating layer being 1.50 to 2.30. 7.The cathode active material for a non-aqueous electrolyte secondarybattery according to claim 6, wherein there is no lithium deficiency inthe coating layer.
 8. The cathode active material for a non-aqueouselectrolyte secondary battery according to claim 6, wherein a specificsurface area of the cathode active material is 0.2 g/m² to 2.0 g/m². 9.The cathode active material for a non-aqueous electrolyte secondarybattery according to claim 6, wherein a particle strength of the cathodematerial is 42 MPa or more.
 10. The cathode active material for anon-aqueous electrolyte secondary battery according to claim 6, whereina moisture content of the cathode active material after the cathodeactive material was exposed in an air atmosphere for 5 days is less than1.1% by mass, and a total carbon amount of the cathode active materialis less than 0.6% by mass.
 11. A non-aqueous electrolyte secondarybattery that is formed using the cathode active material for anon-aqueous electrolyte secondary battery according to claim 6.